Process for producing omega laurolactam

ABSTRACT

A HIGH PURITY W-LAUROLACTAM IS PREPARED FROM A CRUDE CYCLODODECANONE OXIME CONTAINING 5% BY WEIGHT OR LESS OF CYCLODODECANONE BY SUBJECTING THE OXIME TO THE BECKMANN REARRANGEMENT REACTION IN THE PRESENCE OF SULFURIC ACID HAVING A CONCENTRATION OF 98% BY WEIGHT OR MORE OR FUMING SULFURIC ACID CONTAINING 20% BY WEIGHT OR LESS OF SULFURIC-ANHYDRIDE, SEPARATING THE THUS FORMED W-LAUROLACTAM FROM THE REACTION MIXTURE, DISSOLVING THE RESULTING W-LAUROLACTAM N A LIQUID AROMATIC HYDROCARBON, WASHING THE SOLUTION WITH AN ALKALI SOLUTION AT A TEMPERATURE OF 60* TO 120* C., AND RECOVERING W-LAUROLACTAM.

United States Patent 3,767,647 PROCESS FOR PRODUCING OMEGA- LAUROLACTAMToshiro Hirose and Takashi Matsubara, Nagoya, Japan,

assiguors to Toagosei Chemical Industry Co., Ltd.,

Minato-ku, Tokyo, Japan No Drawing. Filed Jan. 11, 1971, Ser. No.105,669

Claims priority, applicsa/tgonogapan, Jan. 19, 1970,

Int. Cl. co7d 41/00 US. Cl. 260-2393 A 4 Claims ABSTRACT OF THEDISCLOSURE The present invention relates to a process for producingextremely pure w-laurolactam.

w-Laurolactam is an-important industrial chemical as the startingmaterial for polyamides. However, for synthesizing w-laurolactam of anindustrial value, an extremely pure lactam is required. w-Laurolactambecomes very unstable if an impurity is present even in extremely smallamount, and tends to discolor or degenerate not only duringpolymerization but also during storage. On the other hand, under moresevere purifying conditions w-laurolactam tends to degenerate orpolymerize during purification, resulting in a loss of the product.

An object of the present invention is to provide a process for producinghighly purified w-laurolactam by an inexpensive procedure withdiminished loss of the lactam.

There have been known, heretofore, a number of purification methods withregard to lactams. For example, for the purification of e-caprolactamthere have been known several methods such as recrystallization fromvarious solvents, treatment with an ion-exchanger, treatment withhydrogen in the presence of a hydrogenation catalyst, treatment withpotassium permanganate, treatment with a reducing agent, extraction,contact with an adsorbent, disillation after addition of a peroxide,etc.

However, each of these methods has a disadvantage such as aninsufficient degree of purification, a high purification cost, etc.Moreover, since w-laurolactam has different properties from those ofe-caprolactam, every above-said method is not always independentlyapplicable to w-laurolactam. For instance, e-caprolactam has a highsolubility in water, i.e., 800 to 900 mg./cc., whereas wlaurolactam hasa solubility of only 0.6 mg./cc. under the same conditions.

With regard to the purification of S-laurolactam, also, a number ofmethods have been known. There have been proposed methods such as, forexample, treatment with an alkali metal hydroxide at a temperaturehigher than 160 C. (Japanesepatent publication No. 21,734/69), treatmentwith a powdered metal or a metal oxide (US. Pat. No. 3,154,540),extraction (Dutch Pat. No. 6,413,- 634), recrystallization (JapanesePat. publication Nos. 3,614/66 and 81/62; Ind. Eng. Chem., 53, 826),hydrogenation (French Pat. No. 1,332,193), treatment with a solidadsorbent (Japanese Pat. publication No. 22,379/ 66), etc. However, eachof these methods has its own defect such as an operational difficulty onindustrial scale,

ice

a specific applicability to lactams produced by selected processes, or ahigh cost.

As a result of extensive researches in the process for purifyingw-laurolactam synthesized by the Beckmann rearrangement fromcyclododecanone oxime which was obtained through cyclododecanone, thepresent inventors found that the presence of cyclododecanone incyclododecanone oxime has a great influence upon the quality ofw-laurolactam. The present inventors have found an entirely novel factthat the presence of cyclododecanone not only brings about loss of thematerial through condensation, decomposition, and degeneration but also,when it amounts above 5% by weight, has an adverse effect upon thequality of w-laurolactam obtained by the Beckmann rearrangement. Basedon the finding it has been further found that pure w-laurolactam may beobtained in a high yield by effecting Beckmann rearrangement reactionunder specific conditions using specific starting material, as disclosedhereunder, and then subjecting the resulting product to a simpletreatment, as mentioned hereunder. Based on these findings, the presentinvention has been accomplished. That is, the present invention providesa process for producing highly purified w-laurolactam, which comprisesthe following steps:

(1) cyclododecanone oxime containing 5% by weight of less ofcyclododecanone and sulfuric acid of a concentration of 98% or more orfuming sulfuric acid containing 20% or less of sulfuric anhydride (S0are made to react in the Beckmann rearrangement step.

(2) After being neutralized or without being neutralized with an alkali,the resulting lactam is dissolved in or extracted with (hereinaftersimply referred to as dissolved for the sake of brevity) with anaromatic hydrocarbon or an organic solvent containing an aromatichydrocarbon.

(3) The organic layer obtained in the preceding step is washed with analkali or an aqueous alkali solution (hereinafter simply referred to aswash with alkali) at a temperature of 60 to C.

(4) The organic layer obtained after washing with alkali in thepreceding step is distilled to yield w-laurolactam.

Each of the above-said steps is further illustrated below in detail.

The reasons for limiting the content of cyclododecanone incyclododecanone oxime for feed to the Beckmann rearrangement step are asfollows: When cyclododecanone is present in cyclododecanone oxime in anamount exceeding 5% a high quality lactam is difiicult to obtain, and inorder to obtain w-laurolactam of sufiicient quality for producing apolyamide of industrial value, a further expensive purification becomesnecessary; and if the sulfuric acid used in the Beckmann rearrangementstep is intended to he recovered by neutralization as an alkali metalsulfate, e.g. ammonium sulfate or sodium sulfate, the quality of therecovered alkali metal sulfate is unsatisfactory for the profitableutilization thereof. The content of cyclododecanone in cyclododecanoneoxime can be reduced to less than 5% by increasing the conversion ofcyclododecanone in the reaction with hydroxylamine, or by decreasing theconcentration of cyclododecanone in cyclododecanone oxime obtained at alow conversion by means of recrystallization, extraction, etc.

The concentration of sulfuric acid to be fed to the Beckmannrearrangement step is also an important factor. When sulfuric acid of aconcentration of less than 98% is used, there occur side reactions, ofwhich hydrolysis is dominant, and the resulting w-laurolactam isdifficult to purify. When fuming sulfuric acid containing more than 20%of free sulfuric anhydride is used, there occurs a decrease in the yieldof the lactam.

Other conditions for the Beckmann rearrangement are not critical. Thereaction temperature is 70 to 140 C., v

and the molar ratio of sulfuric acid to cyclododecanone oxime for feedis preferably 2.0 to 5.0. The Beckmann rearrangement reaction iseffected preferably in such a manner that the oxime is dissolved in asolvent such as carbon tetrachloride, cyclohexane, chloroform, methylenechloride, or the like, and under the predetermined conditions ofreaction the solvent is allowed to evaporate to balance the heat ofreaction with the heat of vaporiza tion.

The viscous reaction liquid, brownish black in color, obtained by theBeckmann rearrangement from cyclododecanone oxime is a solution of thelactam in sulfuric acid. For treating said reaction liquid there hasheretofore been known a method, in which the reaction liquid isimmediately poured into an aqueous solution of an alkali such asammonia, sodium hydroxide, potassium hydroxide, sodium carbonate,potassium carbonate, or the like, to hydrolyze and neutralize at thesame time and to separate w-laurolactam as crystals. There has beenknown another method, in which the reaction liquid is diluted with Wateruntil the concentration of sulfuric acid in the water layer becomes to60% to separate w-laurolactarn as crystals. In some cases, the reactionliquid is treated according to the latter method, and then furtherneutralized with an alkali.

In the present process, w-laurolactam contained in the solution which isobtained by the Beckmann rearrangement, is, after being separated as asolid by treatment in the above-said manner, or without undergoing sucha treatment, dissolved in an aromatic hydrocarbon or in an organicsolvent containing an aromatic hydrocarbon. This dissolving is followedby washing with an alkali to effectively recover and purifyw-laurolactam.

Among aromatic hydrocarbons to be used for dissolving (or extracting)w-laurolactam, benzene, toluene, xylene, ethylbenzene, cumene, etc., arepreferred, but other aromatic hyldrocarbons are not excluded. Thesearomatic hydrocarbons are used each alone or in combinations of two ormore members. They are also used in admixture with other solventsincluding halohydrocarbons such as carbon tetrachloride, chloroform, anddichloroethane, cycloaliphatic hydrocarbons such as cyclohexane;aliphatic hydrocarbons such as n-hexane and n-heptane, etc. The amountof an aromatic hydrocarbon in said mixture with an organic solvent isnot critical, but is, in general, preferably more than When said amountis too small, pure w-laurolactam is, in some cases, difficult to obtain.

The temperature, at which the lactam is dissolved in i an aromatichydrocarbon or an organic solvent containing an aromatic hydrocarbon, isnot critical, but is preferably 50 to 100 C. The extract layer (organiclayer), Which contains mainly w-laurolactarn, is yellow or yellowishbrown in color, whereas the raffinate (water layer) is dark reddishbrown in color. The greater part of impurities move into the waterlayer.

In the present process, the above-said yellow or yellowish brown organiclayer is washed with an alkali at 60 to 120 C. By this treatment theorganic layer turns nearly colorless and becomes transparent. This is asurprising fact found by the present inventors, which has resulted fromthe effective combination of the Beckmann rearrangement and thepurification procedure. The alkalis for use in the alkali washinginclude hydroxide of alkali metals, such as sodium hydroxide andpotassium hydroxide; carbonate of alkali metals, such as sodiumcacbonate and potassium carbonate; and ammonia. These compounds are usedas 0.1 to 50% aqueous solutions. When the alkali treatment is conductedat a temperature lower than 60 C., a satisfactory degree of purificationis ditficult to attain and the concentration of w-laurolactam in theorganic layer also becomes low. On the other hand, when the alkalitreatment is conducted at temperatures higher than 120 C. hydrolysis ofthe lactam takes place acceleratingly, to decrease the yield of lactam.Therefore, in the present invention the organic layer should becontacted with the aqueous alkali solution at a temperature of 60 to 120C. In said temperature range an extremely enhanced effect of the alkaliwashing may be displayed and the greater part of discoloring impuritiesmove into the aqueous alkali solution layer.

The alkali treatment may be conducted continuously by contacting theorganic layer countercurrently with the alkali solution, or batchwise bymixing, standing, and then separating the two layers from each other.Each method can be used according to the circumstances. Before beingtreated with an alkali, the organic layer may be treated with otheragents such as water or an aqueous solution containing 0.1 to 20% of aninorganic acid. It is also possible that the organic layer is treatedwith water after the alkali treatment.

The organic layer thus treated contains very few impurities beside theunreacted cyclododecanone, and is a transparent liquid slightlyyellowish in color.

Distillation of the solvent is conducted under atmospheric pressure orreduced pressure, and then distillation of cyclododecanone andw-laurolactam is conducted preferably under reduced pressure attemperatures below 250 C. in the presence of an inert gas, becausew-laurolactam is unstable to heat and air. w-Laurolactam obtained is asnow-white solid which can be polymerized to yield a white polyamide.

As mentioned above the present process is capable of giving highlypurified w-laurolactam in high yields, and hence, is an extremely usefulprocess from the industrial point of view.

According to the study of the present inventors, the distillation of thesolvent is carried out extremely advantageously in cases where tolueneis used as the solvent, by the following method. That is, the method isto distill toluene while maintaining the pressure of distillation columnat the portion of supplying feed stock under 350 to 600 mm. Hg (abs)inclusive, and preferably 400 to 500 mm. Hg (abs). This method isparticularly effective for applying to a toluene solution containing 1to 50% by weight of w-laurolactam. Toluene can be recovered veryeffectively under the condition without causing the clogging of thedistillation column due to the crystallizing of the lactam and thelowering of the yield due to the polymerization of the lactam.

The invention is further illustrated below in detail with reference toexamples and comparative examples. The results obtained in each of theexamples are summarized in Table 1. The quality evaluation of thew-laurolactam obtained was performed as follows:

0.4 gram of arthophosphoric acid was added to 20 g. of w-laurolactam,and the mixture was allowed to polymerize at 295 C. for 4 hours in asealed tube containing nitrogen. The color of the polymer and therelative viscosity thereof were determined to evaluate the quality ofpolymer.

The color of the polymer was compared with the standard color of thesolution of potassium chloroplatinate and cobalt chloride inhydrochloric acid-water (Hazen number, K-4172). The smaller is the Hazennumber, the less is the discoloration, and hence the quality is better.

The relative viscosity in m-cresol was measured by means of an Ubbelohdeviscosimeter at 25 C. on the solution of 0.1 g. of the polymer, whichhad been extracted with hot methanol and then dried, in 25 cc. ofm-cresol.

EXAMPLE 1 740 grams per hour of a carbon tetrachloride solutioncontaining 8% (by weight; the same shall apply hereinafter) ofcyclododecanone oxime, which contained 2% of cyclododecanone [i.e. 59 g.(0.3 mole) of cyclododecanone oxime per hour], and 98 g./hr. (1mole/hr.) of

100% sulfuric acid Were continuously fed to a reactor equipped with astirrer and an outlet for distilled carbon tetrachloride. The reactiontemperature was maintained at 105:3" C., and the residence time wasadjusted to 60 minutes. The rearrangement reaction of cyclododecanoneThe purified w-laurolactam obtained was polymerized in theabove-mentioned manner to yield a white polymer having a Hazen number of60-80 and a relative viscosity of 1.69.

COMPARATIVE EXAMPLES 1-4 5 oxime was allowed to proceed whilecontinuously distilling the carbon tetrachloride. The dark reddish brownExample w repeated except that cyclododecanm w reaction liquid waspoured into cold water to dilute the oxlme corlltammg 10%cyclododecanone was 4 sulfuric acid to a concentration of 30% and toprecipitate Comparatw? EX1mP1e 1; In Place of Sulfunc acldfw-laurolactam as a solid. After neutralization with 28% 10 Was PQ 111 Cparative Example 2, ammonia, the precipitated crystals were collected byfilifummg Sulfulp acid Contammg 30% of free S03 was used tration. 300grams of the solid obtained was dissolved m comparafive Example 1 placeof toluene, chloroin 2,000 cc. of toluene form was used in ComparativeExample 4. The results The yellowish brown toluene solution was mixedwith obtamed were as shown In Table 500 cc. of 3% aqueous sodiumhydroxide solution at a 15 EXAMPLE 3 AND COMPARATIVE EXAMPLEStemperature of 80 C., shaked, and then left standing to separate intotwo layers. The greater part of discoloring Example 2 was repeatedexcept for the change in temimpurities moved to the aqueous lay r, andthe O g peratures of alkali treatment. The results obtained were layerbecame nearly colorless and transparent. After beas shown in Table 1.ing washed twice with 500 cc. of water, the toluene was The resultsobtained in Comparative Example 5 show removed y evaporation, and thenrectification of w-lauroa high Hazen number, which means a highdiscoloration. lactam was carried out under reduced pressure and nitro-The results in Comparative Example 6 show a low yield gen atmosphere toobtain 143 g. of purified w-laurolactam and a low relative viscosity.

TABLE 1 Percent by weight Temper- Yield of Concenature ofw-lauroti'ation alkali lactam Content Concenof S03 in treatment based onQuality evaluation of cyclotration of turning after exoxime,dodecasulfuric sulfuric Organic solvent traction, percent Hazen RelativeExample No. none acid acid for extraction C. by weight No. viscosity 2100 Toluene 80 96.0 60-80 1 74 0.5 3 Xylene 70-80 95.0 60-80 1.69

80 91.0 120-140 1 68 80 92.0 200-250 1 71 80 72.5 40-60 1. 49 4 80 95.0160-180 1. 60 Example 3 100 95. 0 40-60 1. 72 Comparative Exam 5 15095.0 120-140 1.71 6 140 85. 2 (so-so 1. 49

melting at 151.5 152.5 C. The yield corresponded to 96% based oncyclododecanone oxime. The pure w-laurolactam obtained was polymerizedin the above-mentioned manner to obtain a white polymer having a Hazennumber of 60-80 and a relative viscosity of 1.74.

EXAMPLE 2 1180 grams per hour of a cyclohexane solution containing 5% ofcyclododecanone oxime, which contained 0.5% of cyclododecanone [i.e. 59g. (0.3 mole) of cyclododecanone oxime per hour], and 88 g./hr. (0.9mole/ hr.) of fuming sulfuric acid containing 3% of free 80;; werecontinuously fed to the same reactor as in Example 1. Under theconditions of a reaction temperature of 100:2 C. and a residence time of60 minutes, the Beckmann rearrangement of cyclododecanone oxime wascarried out at atmospheric pressure while continuously evaporating thecyclohexane. The overflowing lactam-sulfuric acid solution wascontinuously fed to a neutralizationextractiori tank (maintained at 80C.) equipped with a stirrer and a cooler. To the tank weresimultaneously fed 740 g./hr. of xylene, 50 l./hr. of gaseous ammonia,and 120 g./hr. of water to efiect neutralization and extraction at thesame time. The reaction liquid was left standing to separate into twolayers, and the organic layer was successively washed with 100 cc. of 1%aqueous sulfuric acid, 100 cc. of 1% aqueous ammonia, and 100 cc. ofWater. Each washing was carried out at 70 to 80 C. The organic layerturned nearly colorless and transparent. After evaporation of thexylene, w-laurolactam was rectified to obtain 56 g./hr. of purifiedw-laurolactam melting at 151.5 to 152.5 C. The yield corresponded to 95%based on the cyclododecano e oxime used as the starting material.

What is claimed is:

1. A process for producing w-laurolactam, which comprises subjectingcyclododecanone oxime containing 5% by weight or less of cyclododecanoneto the Beckmann rearrangement reaction in the presence of sulfuric acidof a concentration of 98% by weight or more or fuming sulfuric acidcontaining 20% by weight or less of sulfuric anhydride, dissolving theresulting w-laurolactam in toluene, xylene or a mixture thereof, washingthe solution with an alkali at a temperature of 60 to 120 C., andsubjecting the washed solution to distillation to remove solvent and torectification to obtain w-laurolactam.

2. A process according to claim 1, wherein the dissolution is effectedat a temperature of 50 to 100 C.

3. A process according to claim 1, wherein the washing is effected by anaqueous solution of an alkali selected from sodium hydroxide, potassiumhydroxide, sodium carbonate, potassium carbonate, and ammonia.

4. A process according to claim 3, wherein the aqueous solution contains0.1 to 50% of the alkali.

References Cited UNITED STATES PATENTS 3,145,198 8/1964 Morbidelli etal. 260239.3 A 2,692,878 10/1954 Kahr 260239.3 A 2,758,991 8/1956Kretze-rs et al. 260-239.3 A 2,883,377 4/1959 Von Schickh et al.260239.3 A 3,060,173 10/ 1962 Von Schickh et al. 260-239.3 A 3,431,2553/1969 Strauss et al. 260-2393 A HENRY R. JILES, Primary Examiner R. T.BOND, Assistant Examiner

